Anatomy and Physiology I

The Nervous System

Basic Structure and Function

Instructor: Mary Holman

Three Basic Functions of the Nervous System

Sensory Function

Sensory or afferent neurons

Integrative Function

Interneurons

Motor Function

Motor or efferent neurons

Fig. 10.2a

Brain

Spinalcord Spinal nerves (31 pairs)

Cranial nerves (12 pairs)

CNS vs PNS Central Nervous System Peripheral Nervous System

Divisions of the Nervous System

Central Nervous System CNS

Brain

Spinal Cord

Peripheral Nervous System PNS

Cranial Nerves

Spinal Nerves

Ganglia

Sensory Receptors

Divisions of the PNS

Somatic Nervous SystemSensory neurons

Motor neurons to skeletal muscle only

Autonomic Nervous SystemAutonomic sensory neurons - visceral

Motor neuron impulses to smooth & cardiac muscle,

glands and adipose tissue

Sympathetic vs. Parasympathetic Motor Divisions

Enteric Nervous SystemEnteric complexes of the gut

Fig. 10.7

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Central nervous system Peripheral nervous system

Cell body

Interneurons

Dendrites

Axon

Axon

Sensory (afferent) neuron

Motor (efferent) neuron

Cell body

Axon(central process)

Axon(peripheral process)

Sensoryreceptor

Effector(muscle or gland)

Axonterminal

Cells of Neural Tissue

• Neurons

The electrically excitable nerve cells

responsible for the functions of the nervous system

• Neuroglia (glia, neuroglia, glial)

Support, nourish, & protect neurons

Fig. 10.1

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Dendrites

Cell body

Axon

Nuclei ofneuroglia

© Ed Reschke

The Neuron

600x

Fig. 10.3

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Cell body

Neurofibrils

Nucleus

Nucleolus

Dendrites

Impulse

Nodes of Ranvier

Myelin (cut)

Axon

Axon

Chromatophilicsubstance(Nissl bodies)

Axonalhillock

Portion of acollateral

Schwanncell

Nucleus ofSchwann cell

Synaptic knob ofaxon terminal

Neuron withMyelinatedAxon

Fig. 10.6

Dendrites

Axon Axon

AxonDirectionof impulse

(a) Multipolar

Centralprocess

Peripheralprocess

(c) Unipolar(b) Bipolar(eyes,nose,ears)

Neuroglia of the PNS

• Schwann Cells

Produce myelin sheath

• Satellite Cells

Support neuronal clusters in ganglia

Fig. 10.4a

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Dendrite

Node of Ranvier

Myelinated region of axon

Axon

Unmyelinatedregion of axon

Neuroncell body

Neuronnucleus

Medullated or Myelinated Axon

Schwann cells

Neurolemma containing nucleus

Fig. 10.4b

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Neurilemma

Myelin sheath

Neurofibrils

Axon

Axon

Node of Ranvier

Myelin

Schwann cellnucleus

© Biophoto Associates/Photo Researchers, Inc.

650x

Schwann Cell

Fig. 10.4c

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EnvelopingSchwann cell

Schwanncell nucleus

Unmyelinatedaxon

Longitudinalgroove

Schwann Cell with non-myelinated Axons

Axon

Fig. 10.5

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Schwanncell cytoplasm

Myelinsheath

Myelinatedaxon

Unmyelinatedaxon

© Dennis Emery

30,000x

Neuroglia of the CNS• Astrocytes

major support cells

provide nutrients, monitor metabolism etc

• Oligodendrocytes myelinate axons in CNS

• Microgliaphagocytic

• Ependymalline ventricles & central canal

produce cerebrospinal fluid (CSF)

Fig. 10.8

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Microglial cell

Axon

Oligodendrocyte

Astrocyte

Capillary

Neuron

Myelinsheath (cut)

Node ofRanvier

Ependymalcell

Fluid-filled cavityof the brain orspinal cord

Neuroglia of CNS

Fig. 10.9

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Neuroglia

Neuroncell body

Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R.G. Kessel and R.H. Kardon. ©1979 W.H. Freeman and Company

SEM 10,000x

Fig. 10.10

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AxonSite of injury Schwann cells

(a)

(b)

(c)

(d)

(e)

Changes over time

Motor neuroncell body

Former connectionreestablished

Schwann cellsForm new myelin sheath

Schwann cell tubeextends distal to injury

Proximal end of injured axon regenerates into tube of Schwann cells

Distal portion ofaxon degenerates

Skeletalmuscle fiber

Axonal Repair